1. Technical Field
The invention relates to spectral imaging devices useful in flight vehicles including space vehicles for acquiring color images of a ground surface.
2. Background Art
Various imaging techniques are well-known in the art. U.S. Pat. No. 4,514,767 discloses a color filter with a computer-controlled imaging device which capable of synchronizing the selection of the color filter with the scrolling of the imaging device. U.S. Pat. Nos. 4,827,528; 4,747,157; 4,551,768 and 4,398,256 disclose the technique of co-adding image pixels to enhance signal to noise ratio, but are not related to spectral filtering. U.S. Pat. Nos. 4,947,446; 4,885,787; 4,574,357; 4,703,513; 4,330,833; 4,707,859 and 4,724,544 disclose various electronic digital image filtering techniques not related to pixel co-adding or spectral filtering. U.S. Pat. Nos. 5,023,921; 4,694,342 and 4,731,864 disclose various spatial filtering techniques not related to pixel co-adding or spectral filtering. U.S. Pat. No. 4,792,231 discloses a laser speckle imaging technique for satellites not related to spectral filtering or pixel co-adding.
During the 1970's, NASA launched a number of LANDSAT spacecraft equipped with multispectral sensors. These sensors, equipped with between four and seven simultaneous spectral channels, mapped the surface of earth at ground resolutions of approximately 30 m. They have been applied to a great variety of investigations of the earth's surface, atmosphere and biosphere. In the 1980's, it has been France that has lead in the further development of orbital multispectral sensing. Imagery acquired with the SPOT satellite has a comparable number of spectral channels to LANDSAT, but the surface resolution has been improved.
During the 1980's, NASA has been pioneering the development of hyperspectral sensors which would De capable of mapping the surface of the earth in more than a hundred simultaneous spectral channels. With this heightened degree of spectral characterization, hyperspectral sensing enables identification of surface materials and much more definitive characterization of earth surface processes than is possible with multispectral sensing. However, the hyperspectral sensing technology presents some formidable instrumental, communications and data processing problems.